1. Field of the Invention
The present invention relates to apparatus for regulating the temperature of a tubular barrel within which an extrusion screw is rotatably carried. More particularly, the present invention relates to apparatus for improved extruder barrel temperature regulation by providing an outer sleeve to encircle the extruder barrel, the sleeve incorporating an interiorly positioned source of heat and having spaced groups of outwardly extending cooling fins, and a plurality of air blowers adapted to provide forced flow of cooling air to respective groups of the cooling fins.
2. Description of the Related Art
Extrusion equipment, such as the type for plasticating and extruding polymeric materials, includes a tubular barrel within which a plastication screw is rotatably carried for transporting within the barrel material to be plasticated. The material is initially provided in pelletized or powdered form, and is introduced into the barrel at one end, whereupon it is transported toward the other end by the rotating plastication screw. External sources of heat are provided on the outer surface of the barrel to heat the barrel, and thereby the material within the barrel, to hasten the softening process whereby the initially solid material is softened by heating to a viscous, flowable state. Resistance heater bands of annular form, helical fluid conduits within the barrel, and the like have been used in the past to provide heat to the barrel.
For certain materials the barrel temperature must be maintained within well-defined limits in order to avoid degradation of the material as a result of excessive heating. Regulation of the temperature of an extruder barrel has taken many different forms. For example, in U.S. Pat. No. 2,774,107, which issued Dec. 18, 1956, to B. H. Davis, there is shown an extruder barrel around which a tubular shell is provided, the shell incorporating internal resistance heating elements and having cooling fins. The cooling fins permit cooling of the barrel by allowing atmospheric air to flow by convection over the cooling fins.
In U.S. Pat. No. 4,154,535, which issued May 15, 1979, to Charles Maillefer, an extruder is disclosed in which a plurality of finned sleeves are provided, each of the sleeves including internal coolant ducts for the circulation therethrough of a cooling liquid for providing barrel temperature control.
In U.S. Pat. No. 4,721,589, which issued Jan. 26, 1988, to Holton E. Harris, an extruder is disclosed which includes a plurality of axially spaced outer jackets, each of the jackets including embedded electrical heating elements as well as embedded cooling coils. Temperature is regulated by controlling the power to the heating elements and the temperature of the coolant in the cooling coils in order to maintain the plasticated material at a desired viscosity level.
Although various heating and cooling arrangements have been proposed for regulating the temperature of an extruder barrel, in order to regulate the temperature of the plasticated material within the barrel, the arrangements heretofore proposed either have slow response times, such as by relying upon convection flow of cooling air, or are excessively complex by virtue of incorporating within sleeves both heat sources and liquid coolant channels.
It is therefore an object of the present invention to provide an improved extruder barrel temperature regulation system whereby separate sources of heat and of cooling are utilized in order to provide faster response to a desired change in barrel temperature.
It is another object of the present invention to provide an improved extruder barrel temperature regulating system that does not require the complexities and liquid leakage problems attendant with liquid circulation systems.
It is a still further objection of the present invention to provide an extruder barrel temperature regulating system in which a quick-acting arrangement is provided to maintain desired temperature profiles in each of a plurality of axially spaced zones along the axial length of the extruder barrel.